User guide

Chelsea Technologies Group
FAST
tracka
User Guide HB179 Issue 7.0
Page
19
of
47
Flash count will increase from 1 to SFC for saturation zone and 1 to DFC for relaxation zone. If
the instrument is configured to deliver only saturation flashes, then no relaxation flashes will be
output.
After collecting the raw data necessary to calculate FRRF parameters, the FAST
tracka
presents the
user with a series of numbers corresponding to the integrated (per flash) excitation and emission
signal for both the saturation and relaxation sequences. These numbers represent the
integrated signal, for each flash in the flash sequence, seen by the reference photodiode and
the photomultiplier detector, respectively. Internally, the FAST
tracka
performs a quick
approximation on these integrated data series in order to provide the user with some realtime
estimate of F
m
and F
0
, in case these values are required for the analogue output channel. In
order to make this approximation, the FAST
tracka
first ratios the emission data against the
excitation data, giving a series of numbers (length = SFC + DFC) representing fluorescence
yield (i.e. the ratio of fluorescence out per excitation light in). This series of fluorescence yield
is used to approximate F
m
and F
0
using the following:
F
m
= the average of the final 10 saturation flash Em/Ex ratios
F
0
= the average of the first two saturation flash Em/Ex ratios
3.14 ANALOGUE OUTPUT
The FAST
tracka
can be software configured to present an analogue voltage representing the
internally approximated F
m
and F
0
on the Auxilliary bulkhead connector. The pin configuration for
the bulkhead connector and all other connectors may be found in the appendix.
In order to accommodate the large dynamic range of the FAST
tracka
, the analogue voltage is
normalised, i.e. the output voltage seen on the bulkhead connector is a normalised
representation of the digital value scaled against a value configured by the user via software.
After each acquisition, the FAST
tracka
sends the approximated F
m
and F
0
data digitally to an
internal DAC, which creates the resulting analogue signal given the pre-programmed scale
factor. This signal is buffered and held on the analogue output pins to await polling by the
external analogue monitoring system.
An example: For the hardware full scale range of 5 volts, if the pre-set F
m
scale is configured as
2.0, and the approximated F
m
is calculated to be 1.4, then the output observed on the F
m
analogue pin will be:
V
out
= ( F
m
/ scale) * full scale = ( 1.4 / 2.0) * 5 volts = 3.5 volts
If for some reason the approximated F
m
and F
0
data exceeds the scale value, the analogue
output will limit to 5 volts with no damage to the internal circuitry. As well, if the internal
approximation returns a spurious value of F
m
and F
0
< 0, the analogue output will swing to 0
volts.
3.15 CTD OPERATION
The FAST
tracka
can be used with a Seabird 911 CTD.